There is known an air conditioner that heats or cools air inside a room of a building or the like through the vapor-compression refrigerating cycle.
An air conditioner of this kind is associated with “the stagnation phenomenon”, in which a refrigerant condenses in a compressor whose temperature has been dropped during a halt of the air conditioner, and dissolves in a lubricant oil. When the operation is resumed with the refrigerant stagnation, the refrigerant suddenly vaporizes and causes oil foaming. Thus, the compressor may draw in the refrigerant and also the lubricant oil, thereby increasing oil loss and inviting poor lubrication of the compressor.
There have been conventionally proposed techniques for preventing the stagnation of a refrigerant in a compressor. One of the techniques proposes mounting a heater externally to the casing of the compressor, so as to heat the lubricant oil in the compressor during a halt of the air conditioner (e.g., see Patent Literature 1). Another one of the techniques proposes open-phase energizing a motor of the compressor to cause a coil to generate heat, so as to heat the lubricant oil in the compressor (e.g., see Patent Literature 2).